---
id: js-setup
title: Building a Desktop Plugin
sidebar_label: Building a Desktop Plugin
---
import useBaseUrl from '@docusaurus/useBaseUrl';

Now that we have the native side covered, let's display the data we're sending
on the desktop side. You can check out the full workflow of building Flipper desktop
plugins here: https://fbflipper.com/docs/extending/js-setup.

<img alt="Custom cards UI for our sea mammals plugin" src={useBaseUrl("img/js-custom.png")} />

## Dynamic Plugin loading

By default, Flipper will start with the plugins it was bundled with. You can
configure it to also look for plugins in custom directories. To do that,
modify the `~/.flipper/config.json` file that is created the first time
you start Flipper and add a newly created directory the `pluginPaths` attribute.

Your file will then look something like this:

```json
{
  "pluginPaths": [
    "~/Flipper/custom-plugins/"
  ],
  ...
}
```

## Installing flipper-pkg

`flipper-pkg` tool helps to define, validate and package Flipper desktop plugins. You can install it globally using:
```
yarn global add flipper-pkg
```
or
```
npm install flipper-pkg --global
```

## Creating the Plugin Package

With the loading part out of the way, we can create the new plugin. For that, first create a new folder inside the custom plugins directory. Then use `flpper-pkg init` to initialise a new Flipper desktop plugin package:

```bash
$ cd ~/Flipper/custom-plugins/
$ mkdir sea-mammals
$ cd sea-mammals
$ flipper-pkg init
```

The tool will ask you to provide "id" and "title" for your plugin. Use "sea-mammals" as "id" and "Sea Mammals" as "title". After that the tool will create two files in the directory: `package.json` and `src/index.tsx`.

Open the `package.json` to check the fields:

1. "$schema" must contain URI identifying scheme according to which the plugin is defined. Currently, Flipper supports plugins defined by the specification version 2 (https://fbflipper.com/schemas/plugin-package/v2.json), while version 1 is being deprecated.
2. "name" must start with "flipper-plugin-"
3. "keywords" must contain "flipper-plugin"
4. "id" must be the same as used on native side, e.g. returned by getId() method in Android plugin. In our case that is "sea-mammals".
5. "flipperBundlerEntry" must point to the source entry point which will be used by "flipper-pkg" to produce the plugin bundle.
6. "main" must point to the place where the produced bundle will be written.
7. "title" and "icon" are optional fields specifying the plugin item appearance in the Flipper sidebar.

For instance:

```json
{
  "$schema": "https://fbflipper.com/schemas/plugin-package/v2.json",
  "name": "flipper-plugin-sea-mammals",
  "id": "sea-mammals",
  "version": "2.0.0",
  "main": "dist/bundle.js",
  "flipperBundlerEntry": "src/index.tsx",
  "license": "MIT",
  "keywords": ["flipper-plugin"],
  "icon": "apps",
  "title": "Sea Mammals",
  "category": "Example Plugin",
  "scripts": {
    "lint": "flipper-pkg lint",
    "prepack": "flipper-pkg lint && flipper-pkg bundle"
  },
  "peerDependencies": {
    "flipper": "latest"
  },
  "devDependencies": {
    "flipper": "latest",
    "flipper-pkg": "latest"
  }
}
```
*See [package.json](https://github.com/facebook/flipper/blob/master/desktop/plugins/seamammals/package.json)*

To ensure there are no errors in the defined plugin, install packages (using `yarn install` or `npm install`) and execute script `lint` (`yarn lint` or `npm run lint`) which shows all the mismatches that should be fixed to make the plugin definition valid.

Now that our package has been set up, we are ready to build a UI for our plugin. Either by using a standardized table-based plugin, or by creating a custom UI.
